1. Field of the Invention
This invention relates to an intra-oral force module used in orthodontic treatment. More specifically, the present invention relates to an orthodontic force module for correcting Class II malocclusions.
2. Description of the Related Art
Orthodontic treatment involves movement of malpositioned teeth to orthodontically correct positions. During treatment, tiny orthodontic appliances known as brackets are connected to anterior, cuspid and bicuspid teeth, and an archwire is placed in a slot of each bracket. The archwire forms a track to guide movement of the brackets and the associated teeth to desired positions for correct occlusion. Typically, the ends of the archwire are held by appliances known as buccal tubes that are secured to molar teeth.
Various types of elastomeric devices, also known as force modules, are commonly used in orthodontic treatment. The resilient force of such modules in tension or compression is typically used to move a tooth or an orthodontic appliance relative to other teeth or orthodontic appliances. As one example, tiny O-ring devices are used as ligatures to secure the archwire in slots of the brackets. As another example, elongated devices, including chain-like modules having a number of interconnected O-ring portions, are sometimes stretched between selected brackets in order to move certain teeth relative to other teeth. Other devices are especially adapted to separate adjacent teeth or to rotate a tooth about its long axis.
Examples of known elastomeric devices are found in U.S. Pat. Nos. 3,530,583, 3,758,947, 4,038,753, 4,950,158 and 5,044,946. U.S. Pat. No. 5,317,074 describes improved elastomeric orthodontic force modules that are made of a material resistant to staining when exposed to foods or beverages such as mustard, tea and coffee.
The orthodontic treatment of some patients includes correction of the alignment of the upper dental arch with the lower dental arch. For example, certain patients have a condition referred to as a Class II malocclusion wherein the lower dental arch is located an excessive distance rearward of the upper dental arch when the jaws are closed. Other patients may have an opposite condition referred to as a Class III malocclusion wherein the lower dental arch is located forward of the upper dental arch when the jaws are closed.
Orthodontic treatment of Class II and Class III malocclusions are commonly corrected by movement of the upper dental arch as single unit relative to movement of the lower dental arch as a single unit. To this end, pressure is often applied to each dental arch as a unit by applying pressure to the brackets, archwires or attachments connected to the brackets or archwires. In this manner, the Class II or Class III malocclusion can be corrected at the same time that the archwires and brackets are used to move individual teeth to desired positions.
Orthodontic force modules made of an elastomeric material have been used in the past to treat a Class II malocclusion by connecting a pair of such force modules to both arches on opposite sides of the oral cavity. In such instances, the force module may be used in tension to pull the jaws together in a direction along reference lines that extend between the points of attachment of each force module. Examples of such force modules include an O-ring or a chain-type module made of a number of integrally connected O-rings.
Conventional elastomeric force modules used in treatment of a Class II or Class III malocclusion are often removable by the patient for replacement when necessary and for cleaning of the teeth. Unfortunately, neglect of the patient to reinstall the force modules seriously retards the progress of treatment. Poor cooperation from the patient can defeat timely achievement of the goals of an otherwise well-planned treatment program, resulting in an additional expenditure of time for both the patient and the orthodontist. Patient cooperation is often a problem with adolescent patients.
A number of devices that are fixed in place in the oral cavity during orthodontic treatment have been proposed in the past to overcome the problems of patient cooperation associated with removable force modules. For example, U.S. Pat. Nos. 3,798,773, 4,462,800 and 4,551,095 disclose a telescoping tube assembly that urges the jaws toward positions of improved alignment. The assemblies are fixed to other orthodontic appliances by the orthodontist, and thus problems of patient non-compliance are avoided. The device shown in U.S. Pat. No. 3,798,773 includes an internal coil compression spring to exert force on the dental arches as the mouth is closed.
A coiled wire spring device used in tension for applying corrective forces between the dental arches is shown in U.S. Pat. No. 3,618,214 and includes, in one embodiment, a pair of fasteners such as eyelets secured to opposite ends of the coiled wire spring. A protective sheath is disposed around the spring. The spring produces a restoring force upon elongation that urges the jaws toward an improved alignment.
Other orthodontic devices for correcting Class II and Class III malocclusions are described in U.S. Pat. Nos. 4,708,646 and 5,352,116. Such patents describe flexible members with swivel end attachments for connection to the upper and lower jaws of a patient. The length of the members is selected such that the member is curved in an arc when the patient's jaws are closed. The inherent bias of the members toward a normally straight orientation provides a force that pushes one jaw forwardly or rearwardly relative to the other jaw.
The commercial embodiments of the devices described in U.S. Pat. Nos. 4,708,646 and 5,352,116 include internal coil spring that are surrounded by a plastic sheath. It has been observed in some instances that the coil spring may break during use after a period of time. Unfortunately, the plastic sheath often hides the broken portion of the spring, such that it is difficult to confirm that the device is working as intended.
Other types of force modules are described in U.S. Pat. Nos. 5,435,721, 5,651,672 and 5,897,313. However, there is a continuing need to improve the state of the art so that a force module can be constructed that provides reliable corrective force as desired by the orthodontist over the expected lifetime of its use. More specifically, there is a desire to reduce as much as possible the likelihood that the force module will fracture after extended periods of use in the oral cavity, so that the treatment program is not interrupted and replacement of the module during the course of treatment is unnecessary.